Physiologic mechanisms that may pertain to initiation and recovery from apneic spells will be studied. Special emphasis is given to apnea associated upper airway obstruction ("obstructive apnea"). We will examine the relation of airway patency (larynx, pharynx) to airway pressure in animal (rabbit) and human cadavers. Additionally, the effects of surface adhesion on airway reopening will be sought. The contractile force of presumed airway maintaining muscles (genioglossus and geniohyoid) will be determined in anesthetized rabbits. The possible synergistic action of these and other airway maintaining muscles (stylopharyngeus) will be evaluated by endoscopic studies in human and rabbit cadavers and in anesthetized rabbits. Respiratory load compensating reflexes of the genioglossus and geniohyoid muscles will be evaluated in denervation studies. Finally, in hospitalized premature and newborn infants we will try to identify the cause of obstructive, mixed obstructive and central apneas that closely follow spontaneous large breaths (sighs). The various physiologic responses which could account for spontaneous recovery from airway obstruction will be evaluated in polygraphic studies. These studies are viewed as relevant to the maturation and development of respiratory control in man and to the clinical syndromes of apnea of prematurity, sleep obstructive apnea and Sudden Infant Death Syndrome (S.I.D.S.).